1. Field of the Invention
Embodiments the invention relate to semiconductor pressure sensor devices used in, for example, various kinds of apparatus for vehicular use, medical use, industrial use, or the like.
2. Description of the Related Art
FIG. 7 is an overall configuration diagram of a semiconductor pressure sensor device 500. The heretofore known semiconductor pressure sensor device 500 includes a semiconductor substrate 51 on the front surface side of which are formed a diaphragm 52a, strain gauge resistors 52, an unshown integrated circuit, and the like, a depressed portion 50 formed in the rear surface of the semiconductor substrate 51, a glass substrate 61 fixed to the rear surface of the semiconductor substrate 51, and a resin case 66 housing the semiconductor substrate 51 and glass substrate 61. A vacuum reference chamber 59 is formed by closing the depressed portion 60 in the semiconductor substrate 51 with the glass substrate 61, thus forming a semiconductor pressure sensor IC chip 501. A metal terminal 69 is provided on the resin case 66, and the semiconductor pressure sensor IC chip 501 is connected to the metal terminal 69 via a bonding wire 68 (an Al wire or Au wire). The glass substrate 61 is fixed to the resin case 66 by an adhesive 67, and the surface of the semiconductor pressure sensor IC chip 501 is coated with a protection material such as silicone gel 70.
An interlayer insulating film which is a silicon oxide film 53, an aluminium wiring layer 54, a TiW film 57 which is an adhesion securing and diffusion preventing layer, and an Au film 58 are disposed stacked on the semiconductor substrate 51. The function of the TiW film 57 which is the adhesion securing and diffusion preventing layer is to improve the adhesion to the aluminium wiring layer 54 and prevent Au atoms of the Au film 58 from diffusing to the aluminium wiring layer 54.
A pressure is applied to the diaphragm 52a, provided on the semiconductor pressure sensor IC chip 501, via a protection material such as the silicone gel 70. The strain gauge resistors 52, being provided on the diaphragm 52a, as previously described, is such that the larger the strain amount of the diaphragm 52a, the more greatly the resistance value of the strain gauge resistors 52 changes. A bridge circuit is configured of the strain gauge resistors 52, and converts a change in resistance to a change in voltage, and the change in voltage is voltage output to the exterior via an analog circuit (an integrated circuit) such as an amplifier circuit.
This kind of semiconductor pressure sensor device 500 is used as an intake pressure sensor which measures the pressure of an intake system of an internal combustion engine of a vehicle or the like, but in recently years, has also been used in detecting the pressure of an exhaust system under tightening environmental regulations and safety regulations. As the semiconductor pressure sensor device 500, when used in measuring the pressure of the intake system, only exposed to comparatively clean air or atomized gasoline, chemical resistance required of the semiconductor pressure sensor device 500 is mainly only the resistance to fuel such as gasoline. Therefore, the electrode and bonding wire of the integrated circuit is configured from aluminium or an alloy made mainly from aluminium, and the surface of the integrated circuit is protected by the silicone gel 70 or the like with high chemical resistance, thereby enabling sufficient securing of the resistance of the integrated circuit surface.
However, as the semiconductor pressure sensor device 500, when used in measuring the pressure f the exhaust system, is also exposed to a corrosive substance generated from a nitrogen compound, sulfide, or the like, exhausted from the internal combustion engine, the resistance to various corrosive substances is required of the semiconductor pressure sensor device 500, and as a measure to respond to the requirement, there is proposed a technology wherein a Ti film and Pd film for preventing corrosion are provided on the surface of an aluminium electrode (see, for example, Japanese Patent Application Publication No. JP-A-10-163608).
Also, with the structure of Japanese Patent Application Publication No. JP-A-10-153508, the resistance to corrosion due to nitrate ions formed from nitrogen oxide contained in an exhaust gas is insufficient, in response to which there is proposed a technology wherein a TiW film is provided on the aluminium electrode as an adhesion securing and diffusion preventing layer, and the front surface of the TiW film is coated with an Au film having high corrosion resistance (see, for example, WO 2007-052335).
Also, Japanese Patent Application Publication No. 2007-251158 describes a configuration (a stepped structure) wherein, in order to prevent a diffusion prevention film from being undercut, the diffusion prevention film projects laterally from a seal film.
The TiW film and Au film coating the front surface of the aluminium wiring layer are formed by sputtering or vapor deposition which is a metal film formation method commonly used in a semiconductor, and wet etching, liftoff, or the like, is used in etching for patterning the formed metal film.
As previously described, a plurality of films, such as the adhesion securing and diffusion preventing layer, formed of the TiW film 57, and the Au film 58 having high corrosion resistance, are formed on the aluminium wiring layer 54 by sputtering or vapor deposition. When wet etching is used in etching the formed films, the formed films are wet etched in order from the top layer using an etching solution appropriate for each layer (the Au film 58 and TiW film 57). Because of this, the side etching of the TiW film 57 which is the adhesion securing and diffusion preventing layer close to the aluminium wiring layer 54 increases. The side etching causes an edge portion of the TiW film 57 between the most front Au film 58 with high corrosion resistance and a passivation film 56 to withdraw inward, thus forming a minute gap 80 which is a recess (FIG. 8). FIG. 8 is a manufacturing process sectional view corresponding to the B portion of FIG. 7.
When a gas reaches this kind of minute gap 80, it is easy for the gas to turn to a liquid 81 by capillary condensation.
Meanwhile, the corrosion of a metal such as the TiW film 57 also progresses due to a nitrogen compound or sulfide in a gaseous state, but it is often the case that the corrosion progression is accelerated by the mediation of moisture. Therefore, in some cases, a nitrogen compound or sulfide, moisture, and the like, in a gaseous state, which have intruded into the minute gap 80, turn to the liquid 81 in the minute gap 80, thereby resulting in the progression of corrosion. The corrosion, combined with galvanic corrosion (corrosion between dissimilar metals), called a voltaic cell, between two metal layers (for example, the TiW film 57 and Au film 58), occurs in an interface 82 between the TiW film 57 and Au film 58. When the corrosion progresses, the adhesion of the Au film 58 (a pad electrode) and TiW film 57 decreases, and exfoliation 83 occurs in the interface 82.
As the adhesion securing and diffusion preventing layer formed of the TiW film 57 is low in corrosion resistance, as previously described, it is difficult to use the adhesion securing and diffusion preventing layer in a harsh environment such as in the exhaust system.
Also, as a liftoff method is such to mechanically separate a metal film when removing a resist, thus forming a pattern, the liftoff method is not suitable for a fine pattern formation to several ten μm.
Also, Japanese Patent Application Publication No. 2007-251158 is not such as to deal with the problem of corrosion when using the structure as a pressure sensor in the exhaust system. Furthermore, it is not described in Japanese Patent Application Publication No. 2007-251158 that the side wail of the TiW film 57 and Au film 58 is formed into a normal tapered shape to be described hereafter, thus preventing the formation of the minute gap 80 and suppressing corrosion.